, reusable foam box. Suitable for bubble and jetted pure-spas. Replacement for S1 cartridge. Replacing the filter elements of paper filters is part of the daily maintenance of the pool. These cleaning and reusable foam filters will reduce your cost. The initial cost of the cartridge is slightly higher than that of standard cartridges, but offers a longer lifespan over time. More durable than paper cartridges, and can be washed and reused multiple times. Size: 10.8 x 7.3 cm. Center hole diameter: approximately 4 cm. Note: Allow 2 hours for the compressed product to fully expand. Color: blue. Material: sponge. Package contents: 16 x filter sponges. Only the above package content is included; other products are not included. Note: Light and display differences may cause slight color variations between the image and the actual item. Measurement allowance: +/- 1-3 cm.